1. Field of the Invention
The present invention relates to an outer casing material for a battery and a lithium secondary battery.
2. Description of Related Art
With increasing portability and reduction in size of electronic apparatuses such as video cameras, laptop personal computers, and mobile phones, requests for a reduction in size and weight have also increased for a battery that is a drive source thereof, and as a result, high-performance lithium secondary batteries have become widely used. In recent years, in order to utilize a lithium secondary battery as an in-vehicle power supply of an electric or hybrid vehicle, scaling up the size of the lithium secondary battery has been studied.
However, there is a limit to a mounting space for an in-vehicle power supply in a vehicle and the shape of the mounting space is also not constant. For this reason, similarly to the case of the electronic apparatus or the like, freedom of shape, size reduction (a reduction in thickness) and reduction in weight are required for an in-vehicle lithium secondary battery. As an outer casing material of such a lithium secondary battery, a packaging container as disclosed in, for example, the following Patent Literature 1 is known. The packaging container of Patent Literature 1 is constituted by laminating an outer layer made of a resin layer, aluminum foil, and an inner layer made of a resin layer, and heat-sealing properties are given to the resin layer of the inner layer. By inserting a cell into such a packaging container and heat-sealing the inner layers, a lithium secondary battery having an excellent degree of freedom of shape and hermetic sealing properties is obtained.
Further, since the in-vehicle lithium secondary battery has a large size compared to a lithium secondary battery for the electronic apparatus and the amount of current used is large, excellent insulation performance is required for an outer casing material thereof. In the following Patent Literature 2, as means for evaluating insulation performance, an abnormality detection device of a battery which detects defects of an inner surface resin layer of a battery outer casing material is disclosed.
However, the insulation performance of an outer casing material for a battery in the related art is still insufficient and further improvement is required.